Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 251340
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
340 AM HST MON MAY 25 2015

.SYNOPSIS...
COOL AND RELATIVELY DRY NORTHEASTERLY WINDS WILL CONTINUE THROUGH
TUESDAY...WITH WINDS GRADUALLY WEAKENING. THESE WINDS WILL CARRY
LOW CLOUDS AND A FEW LIGHT SHOWERS OVER THE ISLANDS...WITH THE
SHOWERS FOCUSING ALONG NORTHEAST FACING SLOPES. FROM TUESDAY INTO
NEXT WEEKEND...WINDS ARE EXPECTED TO BE SUFFICIENTLY LIGHT TO ALLOW
LAND AND SEA BREEZES TO PREVAIL...WITH A SOMEWHAT CLOUDY AND
UNSETTLED WEATHER PATTERN EXPECTED.

&&

.DISCUSSION...
AN UNSEASONABLE POST-FRONTAL WEATHER REGIME PREVAILS THIS MEMORIAL
DAY MORNING...WITH LIGHT TO LOCALLY MODERATE NNE WINDS ADVECTING
SCATTERED TO LOCALLY OVERCAST STABLE LOW CLOUDS OVER THE CHAIN. THE
NNE FLOW IS DUE TO A COMPLEX SURFACE LOW NE OF THE ISLANDS AND A
SURFACE HIGH CENTERED TO THE NNW. LIGHT SHOWERS FALLING FROM THESE
CLOUDS ARE FAVORING N AND E FACING SLOPES AND COASTS...WHILE MANY OF
THE LOW CLOUDS HAVE BEEN SPREADING TO LEEWARD AREAS OF THE SMALLER
ISLANDS...BRINGING PERIODS OF DRIZZLE. LATEST SATELLITE IMAGES SHOW
LOW CLOUDS GENERALLY DECREASING IN COVERAGE UPSTREAM OF OAHU...AND
LESS SO UPSTREAM OF THE OTHER ISLANDS.

WHILE THE FRONT THAT MOVED DOWN THE ISLAND CHAIN FRIDAY AND SATURDAY
IS IN THE PROCESS OF DISSIPATING SE OF THE BIG ISLAND...IT/S
ASSOCIATED MOISTURE...ALBEIT SHALLOW...CONTINUES TO LURK JUST TO THE
S AND SE OF THE BIG ISLAND. FORECAST MODELS INDICATE THAT THIS
MOISTURE WILL MOVE BACK OVER THE ISLANDS LATER THIS WEEK AND
INTERACT WITH A DEVELOPING MID-LEVEL TROUGH...BRINGING MODERATELY
UNSETTLED WEATHER TO THE ISLANDS FOR THE SECOND HALF OF THE
WEEK...AND INTO NEXT WEEKEND.

IN THE BIG PICTURE...A LONGWAVE MID-LEVEL TROUGH AXIS WILL DEVELOP
OVER THE ISLANDS BY MID-WEEK...AND PERSIST INTO THE WEEKEND...
KEEPING SURFACE WINDS ON THE LIGHTER END OF THE SPECTRUM. IN THE
MEANTIME...A RELATIVELY WEAK MID-LEVEL RIDGE WILL EXTEND OVER THE
AREA FROM THE W...KEEPING A SUBSIDENCE INVERSION IN PLACE. ON
TUESDAY AND TUESDAY NIGHT...THE SHARPENING TROUGH WILL ACT TO ERODE
THE SUBSIDENCE INVERSION...WITH THE DEPTH OF BOUNDARY LAYER MOISTURE
GRADUALLY INCREASING INTO NEXT WEEKEND AS THE TROUGH PERSISTS
OVERHEAD. LARGE SCALE FORCING APPEARS TO BE MINIMAL FOR WIDESPREAD
HEAVY SHOWER DEVELOPMENT...AND LIGHT SURFACE WINDS WILL KEEP THE
OROGRAPHIC FORCING AT A MINIMUM AS WELL. HOWEVER...A SURFACE TROUGH
DEVELOPING NEAR THE E END OF THE STATE BY MID-WEEK WILL DRAG THE
RESIDUAL FRONTAL MOISTURE NORTHWARD BACK OVER THE CHAIN...AT THE
SAME TIME A PASSING SHORTWAVE HELPS TO BRING A WEAK SURFACE FRONTAL
BOUNDARY TOWARD KAUAI FROM THE N. THESE MOISTURE SOURCES COULD
PROVIDE THE FUEL FOR SOME LOCALLY HEAVY SHOWERS AS THE SURFACE
TROUGH LINGERS NEAR THE ISLANDS INTO NEXT WEEKEND.

THE SURFACE TROUGH WILL ACT AS A FOCUS FOR CLOUDS AND SHOWERS...AND
KEEP NE TO E SURFACE WINDS RATHER LIGHT. WITH THE LIGHT WINDS...
ISLAND-SCALE LAND AND SEA BREEZES WILL OVERRIDE THE LARGE SCALE
WINDS...ALLOWING CLOUDS AND SHOWERS TO DEVELOP OVER THE INTERIOR
AND LEEWARD PORTIONS OF THE ISLANDS IN THE AFTERNOONS BEFORE
DISSIPATING IN THE EVENINGS. WHILE LEEWARD AREAS ARE EXPECTED TO
CLEAR SOMEWHAT AT NIGHT...WEAK NE TO E SURFACE WINDS ARE EXPECTED TO
BRING SOME CLOUDS AND SHOWERS TO WINDWARD SECTIONS.

&&

.AVIATION...
STABLE N TO NE FLOW WILL CONTINUE TO ADVECT STRATOCUMULUS TOWARDS
THE ISLANDS. CLOUDS AND SCATTERED LIGHT SHOWERS WILL FAVOR NORTH AND
NORTHEAST SLOPES. PARTIAL CLEARING IS ANTICIPATED IN THE AFTERNOON
AND EARLY EVENING HOURS. AIRMET SIERRA FOR MTN OBSC NORTHEAST BIG
ISLAND WILL LIKELY REMAIN NECESSARY THROUGH AT LEAST MID MORNING.

&&

.MARINE...
SMALL CRAFT ADVISORY LEVEL WINDS OR SEAS ARE NOT EXPECTED THROUGH
THE UPCOMING WEEK...EVEN THOUGH SWELLS FROM THE S...SSW...NNE...AND
WNW ARE EXPECTED. OPEN OCEAN SWELL HEIGHTS ARE GENERALLY EXPECTED TO
BE 3 FEET OR LESS...AND WITH LOCAL WINDS REMAINING LIGHT TO
MODERATE...COMBINED SEAS WILL REMAIN BELOW THE 10 FOOT THRESHOLD.

SURF WILL REMAIN SOMEWHAT ELEVATED ALONG S FACING SHORES INTO THE
BEGINNING OF JUNE...AS THE DEVELOPING EL NINO FAVORS LOW PRESSURE
DEVELOPMENT NEAR...AND E OF...NEW ZEALAND. A PEAK IN S SHORE SURF
HEIGHTS IS EXPECTED TODAY AND TUESDAY...WITH THE CONTINUED POTENTIAL
FOR ADVISORY LEVEL HEIGHTS ALONG EXPOSED S FACING SHORES. LATEST
BUOY OBSERVATIONS SHOW INCONSISTENT SPIKES IN ENERGY IN THE 20-22
SECOND BAND AS WELL AS THE 14 SECOND BAND. CONFIDENCE IS NOT HIGH
ENOUGH TO ISSUE AN ADVISORY AT THIS TIME...BUT THE FACT THAT TWO
SEPARATE SWELLS WITH DIFFERENT PEAK PERIODS WILL BE ARRIVING MEANS
THAT SURF WILL BE MORE CONSISTENT THAN USUAL ALONG S FACING SHORES.
LATEST SURFACE ANALYSES AND WAVE WATCH MODEL OUTPUT INDICATE THAT A
NEAR-STORM FORCE LOW NOW BREWING E OF NEW ZEALAND IS PRODUCING A
SWELL THAT WILL ARRIVE NEXT WEEKEND...WITH INITIAL INDICATIONS THAT
THIS SWELL WILL PRODUCE SURF NEAR ADVISORY LEVELS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...BEDAL




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